MOLECULAR-EXCHANGE PROCESSES IN PARTIALLY FILLED POROUS-GLASS AS SEENWITH NMR DIFFUSOMETRY

The self-diffusion properties of hexane confined in porous glass with different filling fractions Were studied by means of pulsed field-grad ient spin echo diffusometry. The spin echo attenuation curves were ana lyzed over a range of 3.5 orders of magnitude. Only for the partially filled sample was the shape of the echo attenuation curves found to de pend on diffusion time. This observation indicates a vapor phase contr ibution to the total diffusional displacements and is interpreted by m olecular exchange between the liquid and vapor phases. The distributio n of molecular residence times in the Liquid phase is evaluated from e xperimental data. A thorough analysis of this distribution function yi elds information about the nature of inhomogeneities of the liquid's s patial distribution inside the porous matrix, including typical sizes of the inhomogeneous regions and characteristics of exchange processes at the liquid/vapor interface. The model is further substantiated by additional computer simulations.